
95
1477K–AVR–08/10
ATtiny26(L)
Figure 51. Analog to Digital Converter Block Schematic
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approxi-
mation. The minimum value represents GND and the maximum value represents the voltage on
the AREF pin minus 1 LSB. Optionally, AVCC or and internal 2.56V reference voltage may be
connected to the AREF pin by writing to the REFS bits in ADMUX. The internal voltage refer-
ence may thus be decoupled by an external capacitor at the AREF pin to improve noise
immunity.
The analog input channel and differential gain are selected by writing to the MUX bits in
ADMUX. Any of the 11 ADC input pins ADC10..0, as well as GND and a fixed bandgap voltage
reference of nominally 1.18V (VBG), can be selected as single ended inputs to the ADC. A selec-
tion of ADC input pins can be selected as positive and negative inputs to the differential gain
amplifier.
If differential channels are selected, the differential gain stage amplifies the voltage difference
between the selected input channel pair by the selected gain factor. Note that the voltage on the
positive input terminal must be higher than on the negative input terminal, otherwise the gain
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15
0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL. & STATUS
REGISTER (ADCSR)
ADC DATA REGISTER
(ADCH/ADCL)
MUX2
ADIE
ADFR
ADSC
ADEN
ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
MUX3
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
MUX DECODER
MUX4
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
REFS0
REFS1
ADLAR
+
-
CHANNEL
SELECTION
GAIN
SELECTION
ADC[9:0]
ADC
MULTIPLEXER OUTPUT
GAIN
AMPLIFIER
INTERNAL 1.18 V
REFERENCE
PRESCALER
SINGLE ENDED /
DIFFERENTIAL SELECTION
GND
POS.
INPUT
MUX
NEG.
INPUT
MUX
ADC10
ADC9
ADC8
INTERNAL
2.56 V
REFERENCE
VCC
AREF